The Jackhammer automatic shotgun was developed by the US firearms designer John Andersen, who requested patents for the basic design of this shotgun in 1984. Since that time and until the late 1990s he continued to develop and improve his basic design but as far as I know failed to attract any serious buyers. In fact, only few working prototypes of the Jackhammer were ever built. Some sources stated that only two fully automatic prototypes are exist, and the Jane's Defense Library 2000 stated that the development is complete but production never began. At my opinion, the Jackhammer is a solution that still to have a question, and it possess some questionable features that can distract any serious military or police buyer. But, anyway, it is interesting design and well deserves its place both here and in the general firearms history.
The Jackhammer is a gas operated, fully automatic only shotgun. The gas system of the Jackhammer consists of the gas cylinder, formed around the movable barrel.